Timing belt tensioners maintain precise belt tension around the crankshaft and camshaft sprockets, ensuring correct engine valve timing. Typically located near the timing belt or chain, these components utilize spring pressure or hydraulic force to automatically adjust for belt stretch or wear. Designs include fixed, spring-loaded, and hydraulic varieties, often incorporating a rotating pulley or idler arm. Failure can result in improper timing, engine damage, or complete belt failure. Regular inspection and replacement are critical during scheduled maintenance, particularly in interference engines.